This research is concerned with the short- and long-term effects of delta 9-tetrahydrocannabinol (THC) on maternal behavior and infant development in the squirrel monkey (Saimiri sciureus), and how such changes might be related to certain physiological events, e.g., the presence and time course of THC and its metabolites in mothers' milk. Mothers receive the drug via different routes and at different dosages, interdrug intervals, and postnatal periods. Maternal and infant behaviors are then evaluated with respect to mother-infant interactions and interactions with other animals, as a function of the drug conditions. This is accomplished by making observations of social and individual behaviors with standard procedures as well as by using tests designed to measure specific aspects of behavior, e.g., maternal care. Various physiological changes, such as the excretion of radiolabeled delta 9-THC in the milk of nursing mothers, are also determined as a function of the drug-related variables and correlated with behavioral changes.